Equation of a line/linear boundaries: Udacity course

I’ve just started the PyTorch course on Udacity and have stumbled already at the first video! The section is linear boundaries and uses the example of university admissions to show the distribution of students who were admitted on one side of the line, and those who failed to be admitted on the other.

I just don’t have any idea where they came up with the equation for the line as being 2x1 + x2 - 18=0.
Is this the standard equation of a line? It’s been ages since I did maths and a quick google doesn’t turn this up as the standard equation.

I’ve just attached an image of the distribution from the course in case this is helpful.
Please be as brutal as need be if you think my maths needs to be refreshed before I continue and if this is something I should already know.

If you look for “Linear Equation”, you’ll find this Wikipeida article that has the same form (a_1 x_1 + a_2 x_2 + b = 0) if you set a_1 = 2, a_2 = 1, b= -18.
There are various interpretations there that might help.

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